Scrub the potatoes, then while they are still damp dust them lightly with salt and leave them to dry for a few minutes. Bake them at 200 C/gas mark 6 until the skin is crisp and the inside soft and fluffy - a matter of 45 minutes to an hour, depending on the variety of the potato.

Half an hour or so before you expect the potatoes to be ready, start cooking the leeks. Split the leeks in half, wash them thoroughly, then cut them into finger-thick slices. Melt half the butter in a heavy pan, add the leeks and let them cook, slowly and covered with a lid over a low heat, until they are soft and translucent.

Split the potato in half and scoop the flesh into a mixing bowl, then drop in the leeks, the remaining butter and most of the cheese, and beat to a creamy mass with a wooden spoon or electric beater. Taste and season with salt and black pepper. Pile back into the skins, dot the last of the cheese over and return to the oven for a good 15 minutes until piping hot.

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